CHST Excavation and Trenching Safety 2 — Questions and Answers

Question 1: Under OSHA 1926.650, what is the definition of an 'excavation'?

Any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal (Correct answer)
Only cuts in the ground deeper than 4 feet
Any underground work area where workers are present
A trench that is at least as wide as it is deep

Correct answer: Any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal

OSHA 1926.650 defines an excavation as any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal, regardless of depth.

Under OSHA 1926.650(b), an excavation is defined as any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal. This definition includes trenches. A trench is a narrow excavation where the depth is greater than the width but does not exceed 15 feet measured at the bottom. Protective systems are required for excavations 5 feet or deeper unless the excavation is made entirely in stable rock.

Question 2: Which OSHA soil classification represents the least stable, most hazardous condition for excavation work?

Type C (Correct answer)
Type A
Type B
Stable Rock

Correct answer: Type C

Type C is the least stable soil classification under OSHA 1926.652, requiring the most conservative protective system design. It includes cohesionless soils like gravel, sand, and loamy sand, and soils subject to water seepage.

OSHA Appendix B to Subpart P classifies soils from most to least stable: Stable Rock, Type A, Type B, and Type C. Type C soils include cohesionless soils (gravel, sand, loamy sand), submerged soil or rock, soil from which water is freely seeping, and soils in environments where fissuring is present. Sloping in Type C soil requires a maximum slope of 1½H:1V (34 degrees), the shallowest and most conservative slope requirement.

Question 3: How far must excavated soil and materials (spoil pile) be kept from the edge of an excavation under OSHA 1926.651?

At least 2 feet from the edge (Correct answer)
At least 3 feet from the edge
At least 5 feet from the edge
At least 4 feet from the edge

Correct answer: At least 2 feet from the edge

OSHA 1926.651(j)(2) requires that excavated material and equipment be kept at least 2 feet from the edges of excavations to prevent cave-in hazards from surcharge loads.

Spoil piles placed too close to an excavation edge add surcharge pressure to the trench wall, increasing the risk of cave-in. OSHA 1926.651(j)(2) mandates a minimum 2-foot setback for excavated materials and equipment from the edge. Even beyond 2 feet, heavy equipment and stockpiles can still create hazards, and the competent person should evaluate the impact of nearby loads on trench stability.

Question 4: Under OSHA 1926.651(c)(2), at what trench depth must a stairway, ladder, ramp, or other safe means of egress be provided?

4 feet or more in depth (Correct answer)
6 feet or more in depth
5 feet or more in depth
8 feet or more in depth

Correct answer: 4 feet or more in depth

OSHA 1926.651(c)(2) requires adequate means of egress in trench excavations 4 feet or more in depth, with the egress point no more than 25 feet of lateral travel from any worker.

Workers in trenches 4 feet or deeper must have safe means of egress — a stairway, ladder, ramp, or other approved device — within 25 feet of lateral travel. This allows workers to escape quickly in the event of a cave-in or other emergency. Multiple egress points may be needed in long trenches. Ladders must extend at least 3 feet above the top of the excavation and must be secured to prevent displacement.

Question 5: What must be done before excavation work begins near underground utilities under OSHA 1926.651(b)(3)?

Contact utility companies and use detection equipment to determine the location of underground utilities (Correct answer)
Assume utilities are absent if no records exist
Dig slowly and stop if you hear or feel any resistance
Utilities only need to be marked if the excavation is deeper than 5 feet

Correct answer: Contact utility companies and use detection equipment to determine the location of underground utilities

OSHA 1926.651(b)(3) requires that the approximate location of underground utilities be determined before opening an excavation, using utility notification systems (811 call), records, and detection equipment.

OSHA requires employers to contact utility companies or owners to determine the approximate location of underground utility installations before excavating. In the US, calling 811 (the national 'Call Before You Dig' number) is the standard way to initiate utility locates. However, marked locations are estimates, and OSHA requires hand-digging or other safe excavation methods within the tolerance zone near marked utilities to avoid striking buried electrical lines, gas mains, or other utilities.

Question 6: Under OSHA 1926.651(g)(1), what must be done before workers enter an excavation greater than 4 feet deep where a hazardous atmosphere may exist?

Test the atmosphere for oxygen content, flammable gases, and toxic substances before entry (Correct answer)
Post a warning sign at the entrance
Ventilate continuously regardless of test results
Send one worker in to confirm safety before others enter

Correct answer: Test the atmosphere for oxygen content, flammable gases, and toxic substances before entry

OSHA 1926.651(g)(1) requires testing for oxygen deficiency, flammable gases, and toxic substances before workers enter excavations over 4 feet deep where a hazardous atmosphere may exist, and as often as necessary to ensure safety.

Excavations can accumulate hazardous atmospheres from nearby sewer lines, fuel tanks, underground utilities, or soil off-gassing. OSHA 1926.651(g)(1) requires testing for oxygen levels (acceptable range 19.5 to 23.5%), flammable gases (below 10% of LEL), and toxic substances before entry into excavations over 4 feet. Testing must be repeated as conditions change. Emergency rescue equipment must be readily available when hazardous atmospheric conditions could be present.

CHST Excavation and Trenching Safety 2

Under OSHA 1926.650, what is the definition of an 'excavation'?